In this project studies will be carried out first to examine and characterize the cell metabolism in an isolated defined segment of single nephron obtained from rabbit, rat, and human kidneys, and then evaluate the ionic and hormonal regulation of cell metabolism. More specifically, the following experiments will be done in each segment, i.e., proximal convolution, pars recta, thick ascending loop of Henle, segments of connecting tubules, and cortical collecting tubules. 1. Define the basic metabolic characteristics. 2. Examine effects of changes of H ion, Ca ions, and phosphate in the extracellular milieu on cell metabolism. 3. Identify the hormone-sensitive nephron segments by assaying adenylate cyclase activity, or by measuring the receptor-mediated hormone degradation (insulin). 4. Examine changes in cell cyclic AMP in response to parathyroid horm ne, calcitonin, catecholamines, antidiuretic hormone, and insulin, alone or in combinations, and the modulating effects of changes of the ionic composition of extracellular milieu. 5. Determine the effects of parathyroid hormone, calcitonin, and other hormones, and cyclic AMP on cell metabolism in each hormone-sensitive segment of nephron. 6. Initiate studies on the changes in the oxidation of metabolic fuels when tubule segments are perfused in an effort to gain insight into the coupling between cell metabolism and transepithelial solute transport. These studies will provide further information on the characteristics of renal cell metabolism in each defined nephron segment, its control by ions and hormones, and on the species difference (i.e., rabbit, rat, human). The studies may also help understand the mechanisms of action of parathyroid hormone and calcitonin and other hormones, and the relative roles of cyclic AMP and calcium ion as intracellular mediators of hormone action, and the relation between tubule cell metabolism and transport function.